Like Cleopatra herself, Arsinoe lived her short life in the internecine maelstrom of Ptolemaic politics under the sway of a Roman Empire itself immersed in civil strife. Violent death was something of an occupational hazard.

Nevertheless, had some flash of prescient irony visited her when Antony’s legionaries unsheathed their blades, she might well have wondered at the small happenstances of fate that left her a nigh-forgotten footnote in her sister’s story, rather than the other way around.

Three siblings had grasped at the Egyptian throne during the Alexandrian War, and whether it was charm or cold calculation won Caesar’s backing for Cleopatra, Arsinoe and her brother Ptolemy XIII still pressed the Roman garrison of Alexandria with a vastly superior force in a battle that was said to have set the Library of Alexandria aflame.

Timely Roman reinforcements decided the matter, and Arsinoe was marched in chains at Caesar’s sumptuous quadruple Triumph of 46 B.C.E. — though she was spared the execution that typically concluded such an ignominy and instead packed off to a temple on the coast of modern-day Turkey.*

In Margaret George’s historical novel The Memoirs of Cleopatra, the danger of maintaining an enemy who has styled herself Queen is neatly summarized in a conversation between Caesar and Cleopatra set after the Triumph:

“I have spared Arsinoe.” [said Caesar]

My [Cleopatra’s] first feeling was a rush of relief. My second was worry. Arsinoe the proud would not retire quietly.

“Where is she to go?”

“She has requested sanctuary at the great Temple of Diana in Ephesus,” he said. “And I will grant it, if you agree.”

Ephesus! Too close to Egypt! Better send her to Britain! Yet … I would gamble, and be merciful. Perhaps I was not enough of a Ptolemy after all. Arsinoe would not have granted it.

“Yes, I will allow it.”

That very perception of her potential danger hung over Arsinoe like the sword of Damocles.

The sword fell — figuratively and literally — five years later after Cleopatra seduced Mark Antony at Tarsus in the autumn of 41. Her terms for Egypt’s alliance supposedly included elimination of this lingering rival — though if Arsinoe had made common cause with Caesar’s Republican assassins, Antony may well have had his own reasons to dispatch the young woman.

Arsinoe’s death helped seal a pact that was itself destined for a bloody end. Distracted by his foreign paramour, Antony steadily lost political ground to his adversary Octavian. In another decade’s time, open war broke out again.

The Egyptian fleet would gather at Ephesus, not far from Arsinoe’s final resting place, bound for the catastrophic Battle of Actium whose outcome added Cleopatra’s and Antony’s blood to the soil from which sprung the long reign of Octavian — soon to be styled Augustus Caesar, the first emperor of Rome.

* A Temple of Artemis — either in Miletus (as Appian has it), or the wonder of the world in Ephesus (as Josephus has it). She met her death at the temple — whichever it was — dragged to its steps and put to the sword. Ephesus seems to be the more generally accepted locale, and an octagonal tomb there has been speculativelyidentified as Arsinoe’s.